Generating oscillations device



Jlily 17, 1934. 5 5 DAVID 1,966,616

GENERATING OSCILLATIONS DEVICE Filed Nov. 5, 1950 Zzzbazfiior ?atentedJuly 17, I934 curries stares fearENr orrics i.

1,966,616- GENERATING OSCILLATIONS DEVICE Pierre Bernard Francois David,Paris, France Application November 5, 1930, Serial No. 493,657

in France November 23, 1929 4 Claims.

A number of ways are known in which to connect three electrode valves incircuits including inductance and capacity for the purpose of generatingoscillations.

In these circuits the frequency generated is in the neighbourhood of thefrequency proper to the circuit but not exactly equal thereto. A slightdifference exists between them, variable with the heating, the,potential applied to the plate, the resistance of the circuit etc.,which gives the emissions a certain very objectionable irregularitywhich may exceed the hundredth part of the frequency.

It is known to diminish this drawback somewhat by hnparting a negativebias to the grid, either by means of a special battery or by inserting ahigh resistance in its circuit shunted by a condenser such as to allowthe oscillations to pass. In efiect, since the grid current becomesappreciable as soon as the grid is positive, the fall of potentialacross the resistance automatically lowers the mean potential of thegrid.

Finally valves are known which have more than one grid and which ingeneral fulfill different functions.

For example one of the grids receives the impulses to be amplified ordetached whilst the other which is kept at a fixed potential acts on thespace charge and diminishes the internal potential of the valve. Againone of the grids is connected to the aerial, whilst the other isconnected to the plate to produce local oscillations which act with theoscillations received to produce a change in frequency.

Bearing these various points in mind the present invention has for itsobject to provide a method of connecting a two grid valve to generateparticularly stable oscillations, that is to say so that the accidentalvariations of frequency resulting from variations in the potentialsupplied, or replacement of valve etc., are very considerably reduced ingeneral to something of the order of one hundred thousandth of thefrequency produced.

' This method of connection consists in giving the same control functionto both grids. Several elements are arranged in such manner that theelectrons must traverse them successively in thepath from the filamentto the anode. This provides a regulating field which is not simply .asurface but a volume.

The different elements are all coupled to the plate circuit and partakeof the same variations of alternating potential, with different biases.

Without entering into the theory of valves of this kind which isdoubtless very complicated, it is conceivable that the control effectexerted on the electronic current by a single grid should bestrengthened and multiplied by traversing several grids in succession.If for example the character istic is drawn for the plate of a valve soconnected, it is found to be of the form C of Figure 1. By comparisonwith the curve C for an ordinary valve, it will be seen thattheamplification is increased, since the curve rises more steeply, butabove all that it is much more sharply bent and thatthe plate currentcommences only at considerably high grid potentials.

Similar observations could be made concerning the characteristics of thegrid; As soon as the potential becomes positive the two grids which areconnected take a considerable current which is evidently greater than istaken by a single grid.

Now very pronounced bends in the characteristic are extremely favourableto the stability of the frequency because they make the currents varyconsiderably from the sinusoidal form.

For example suppose AB is the amplitude of the alternating variation ofthe grid potential (Figure 2) Suppose a considerable resistance isinserted in the grid circuit. As soon as the instantaneous potentialbecomes positive a current passes and a potential drop is producedacross the resistance. The mean potential decreases to approximately thevalue OM. The plate current is therefore strictly zero thoughout thegreater portion of the period (distance A0). Current passes only duringa very short interval (distance OB) Its form is therefore that indicatedin Figure 3 having extremely short peaks. This is what is observed whenexamining the current .by oscillograph.

The result of this is that the oscillations are generated by very shortimpulses applied to the oscillatory system and this is precisely theideal condition required in order not to disturb the natural frequency,a condition that is always aimed at particularly in the case ofpendulums. The arrangement herein disclosed enables this effect to beobtained in a very much more marked degree than the presentarrangements, giving appreciable power at low potentials.

It is to be observed that similar phenomena can be produced with anordinary valve having a simple grid, but if it is desired to impress atrue impulse on the oscillating circuit it is neccsscary to reduce thetime during which the anode current I passes with the flattened form ofthe characteristic C (Fig. 1) and this necessitates maintaining the gridat a strongly negative mean potential, and leads to this currents havingsuch small maximum values that the oscillating current generated by thevalve is of insignificant intensity. With the device according to theinvention the sharply bent form of the characteristic 0 lators andparticularly to symmetrical or push pull circuits which presentadvantages for very short waves, but are subjected to the samevariations of frequency.

The following description and the accompanying drawing illustrate by wayof example different ways of carrying out the invention.

Figures 1 to 3 are curves explaining the operation of the valve.

Figures 4 and 5 show two circuits for a two grid valve of which thegrids are at different constant potentials.

Figures 6 and 7 show two circuits of the type known as push pull.

The valve (Figure 4) comprises an envelope 1 in which is a filament 2heated by current from a battery 3, a plate 4 and two grids 5 and 6. Theplate is connected to the filament through an oscillatory circuit 7 anda battery 8. The grids are connected to the filament in different waysthrough inductances 12 connected to the oscillatory circuit 7. Accordingto the arrangement shown in Figure 4, each of the grids is maintained ata negative potential relative to the filament by means of specialbatteries 9 and 11, the positive poles of these being connected to twodifferent variable points along the inductance and thence to theoscillatory circuit 7, the inductance 12 being connected directly to thefilament.

Figure 5 shows a modification of the above described circuit in whichthe inductance 12 is connected to an intermediate point of a battery 8and in which the batteries 9 and 11 are replaced by resistances 13 and15 shunted by condensers l4 and 16 for lowering the potential of thegrids.

As long as no oscillation is generated, the grids have potentials whichare positive relatively to the filament, but by giving a great enoughvalue to the resistances 13 and 15, it is possible to cause theoscillating potentials of the grids to keep negative mean values.

Figures 6 and 7 show how a two grid valve may be employed in a push pullcircuit.

In Figure 6, the two grid valves 1, 1' have the grids polarized bybatteries 9, 11 and 9', 11, respectively. The grids of each valve areconnected at the extremities of the coil 12, the middle of which isconnected to the filaments and which is coupled to the circuit 7connecting the two plates and connected by the mid-point of theinductance to the anode battery 8.

Figure '7 shows a modification of the same circuit. The coil 12 isomitted and the grids are connected to different points of theinductance of the circuit 7. The negative bias or polarizing batteriesare omitted and replaced by resistances 13, 15, 13, 15 shunted bycondensers 14, 16, 14', 16'.

This arrangement has the advantages that it requires only one inductancecoil.

The last two arrangements to be described are" particularly suited forshort waves.

I claim:-

1. An oscillations generating device of the type wherein an oscillatorycircuit is excited by short impulses of current, comprising a vacuumtube, inside said tube a heated filament, a plate, and two gridsarranged between said filament and said plate, an electric potentialsupply, means for connecting the negative pole of said supply with saidfilament, and the positive one with said plate, circuits connecting saidtwo grids to said filament, an oscillatory circuit in the plate circuit,means for coupling this oscillatory platecircuit to the twogrid-circuits in such a manner that this coupling is sufficient to setup and maintain steady oscillations, means for applying to both gridsdififerent biasses, the mean values of which are constant and negativeduring oscillation.

2. An oscillations generating device 01" the type wherein an oscillatorycircuit is excited by short impulses of current, comprising a vacuumtube, inside said tube a heated filament, a plate, and two gridsarranged between said filament and said plate, an electric potentialsupply, means for connecting the negative pole of said supply with thefilament, and the positive one with the plate, circuits connecting saidtwo grids to said filament of an oscillatory circuit in theplatecircuit, means for coupling this oscillatory platecircuit to thetwo grid circuits in such a manner that this coupling is sufficient toset up and maintain steady oscillations, two batteries arranged forapplying to both grids different biassing po-- tentials, the mean valuesof which are constant and negative during oscillation.

3. An oscillations generating device of the type wherein an oscillatorycircuit is excited by short impulses of current, comprising a vacuumtube, inside said tube a heated filament, a plate, and two gridsarranged between said filament and said plate, an electric potentialsupply, means for connecting the negative pole of said supply with thefilament, and the positive one with the plate, circuits connecting saidtwo grids to said filament, an oscillatory circuit in the plate circuit,means for coupling this oscillatory platecircuit to the two gridcircuits in such a manner that this coupling is sufiicient to set up andmaintain steady oscillations, between each grid and the said filament acondenser shunted by a resistance, the values of these elements beingsuch that during oscillation the mean values of the two grid potentialsare constant, negative and diiierent one from the other.

4. A push-pull oscillations generating device comprising two vacuumtubes having each a heated filament, a plate, and two grids arrangedbetween said filament and said plate, an oscillatory circuit comprisingan inductance coil and a condenser connected in parallel, means toinsert said circuit between the plates of said vacuum tubes, means forconnecting the filaments to the middle point of the inductance coil,means for connecting the grids with different points of said inductioncoil, and means for maintaining during oscillation the potentials ofboth grids of each tube at negative mean values, which are constant anddiiferent one from the other.

PIERRE BERNARD FRANCOIS DAVID.

